Preparation method for electromagnetic wave shield composite material using copper- and nickel- plated carbon fiber prepared by electroless and electrolytic continuous processes, and electromagnetic wave shield composite material

ABSTRACT

The present invention relates to a preparation method for an electromagnetic wave shield composite material and the electromagnetic wave shield composite material prepared by the method. The present invention uses a highly conductive carbon fiber prepared by electroless and electrolytic continuous processes, and thus is suitable for an EMI shield due to having an excellent conductivity and low surface resistance, and is capable of providing the electromagnetic wave shield composite material having an excellent productivity and economic value. Furthermore, the electromagnetic wave shield composite material of the present invention can be used for blocking electromagnetic waves by being inserted into a cell phone cover and a cell phone pouch, and can also be applied to a bracket for protecting an LCD of a portable display product.

FIELD

The present patent application claims priority to and the benefit ofKorean Patent Application No. 10-2013-0062962 filed in the KoreanIntellectual Property Office on May 31, 2013; and Korean PatentApplication No. 10-2013-0159979 filed in the Korean IntellectualProperty Office on Dec. 20, 2013, the disclosures of which areincorporated herein by reference.

The present invention relates to preparation method for electromagneticwave shield composite material using copper- and nickel-plated carbonfiber prepared by electroless and electrolytic continuous processes, andelectromagnetic wave shield composite material.

BACKGROUND

With the rapid development of the computer and electronic informationindustry and the appearance of vehicles and high-speed trains equippedwith advanced electronic equipment in the 21st century, electromagneticwaves generated from various electronic products mutually influenceelectronic devices. For example, in some cases, the defects of thevehicle's electronic system in Japan, which were an international issuein early 2010, and the failure of the high-speed rail systems in Korea,were found to result from electromagnetic waves, and the electromagneticwaves may also cause loss of lives.

Moreover, there are a series of medical reports that electromagneticwaves directly cause serious harm to the human body. Theseelectromagnetic waves are classified into high-frequency electromagneticwaves generated from various home appliances, such as mobile phone,radar, TV, and microwave, and low-frequency electromagnetic wavesgenerated from household and industrial power generation, andparticularly, electromagnetic waves generated at the high-frequency bandof 100 MHz to several GHz cause harm to humans.

The unit to express the electromagnetic shielding effect is designatedby decibel (dB), which means the electromagnetic intensity ratio beforeand after shielding. The effectiveness of 20 dB means the reduction inthe amount of electromagnetic waves to 1/10, and the effectiveness of 40dB means the reduction in the amount of electromagnetic waves to 1/100.It is generally determined that the shielding effect is favorable at30-40 Db or more. In order to protect electronic devices and humanbodies from the harm caused by the generation of electromagnetic waves,the regulations have been strengthened around the globe, and respectivecountries are strengthening EMI regulations.

Following this trend, a metal substrate is used, or a conductive coatingor plating is applied to the substrate, for electromagnetic shielding.The metal substrate has disadvantages in that the processing ofcomplicated patterns is difficult and it's heavy in weight. Moreover,the method of substrate plating is not advantageous in the productivitydue to complicated processes therefor, such as degreasing, etching,neutralizing, activating, accelerating, metal depositing, activating,and primary to tertiary plating. Moreover, shielding materials using afiller, such as carbon nanotubes, a metal powder, graphite, or ferrite,have been reported, but they show defects in dispersibility,processability, electromagnetic shielding efficiency, and the like.Metal plating is applied to the filler in order to solve thedisadvantages, but such a plating manner of a conductive powder isdifficult for practical use due to a delicate process, productivity, andhigh production prices.

As for recent technologies associated with electromagnetic shielding,U.S. Pat. No. 5,827,997 discloses the complexation of nickel fibers, orcarbon filaments plated with nickel through electroplating, with apolymer resin; US Publication No. 2002/0108699 discloses thecomplexation of conductive fibers with a resin; Korean PatentApplication No. 10-2009-0031184 discloses an electromagnetic shieldingfilm containing carbon nanotubes; Korean Patent Application No.10-2006-0039465 discloses a method for manufacturing an electromagneticshielding film; Korean Patent Application No. 10-2000-0039345 disclosesan electromagnetic shielding material using carbon nanotubes or carbonnanofibers; and Korean Patent Application No. 10-2009-0057726 disclosesa method for preparing a polymer/carbon nanotube composite withexcellent electromagnetic shielding efficiency.

Throughout the entire specification, many papers and patent documentsare referenced and their citations are represented. The disclosures ofcited papers and patent documents are entirely incorporated by referenceinto the present specification, and the level of the technical fieldwithin which the present invention falls and details of the presentinvention are explained more clearly.

DETAILED DESCRIPTION Technical Problem

The present inventors have endeavored to develop a composite with anexcellent electromagnetic shielding performance. As a result ofmanufacturing a molded product by mixing copper- and nickel-platedcarbon fibers obtained by continuous electroless and electrolyticprocesses and a thermoplastic resin or a thermosetting resin, and thenperforming injection, extrusion, or discharge molding on the mixture, anexcellent electromagnetic shielding effect as well as superioreconomical feasibility and productivity was confirmed.

Accordingly, an aspect of the present invention is to provide a methodfor preparing an electromagnetic shielding composite using athermoplastic resin and copper- and nickel-plated carbon fiber preparedby electroless and electrolytic continuous processes.

Another aspect of the present invention is to provide a method forpreparing an electromagnetic shielding composite using a thermosettingresin and copper- and nickel-plated carbon fiber prepared by electrolessand electrolytic continuous processes.

Another aspect of the present invention is to provide an electromagneticshielding composite prepared by the method of the present invention.

Other purposes and advantages of the present disclosure will becomeclarified by the following detailed description of the invention,claims, and drawings.

Technical Solution

In accordance with an aspect of the present invention, there is provideda method for preparing an electromagnetic shielding composite, themethod comprising:

(a) mixing 50-90 wt % of a thermoplastic resin and 10-50 wt % of copper-and nickel-plated carbon fibers obtained by continuous electroless andelectrolytic processes; and

(b) performing injection or extrusion molding on the product in step (a)to obtain an electromagnetic shielding composite.

In accordance with another aspect of the present invention, there isprovided a method for preparing an electromagnetic shielding composite,the method comprising:

(a) mixing 50-90 wt % of a thermosetting resin and 10-50 wt % of copper-and nickel-plated carbon fibers obtained by continuous electroless andelectrolytic processes; and

(b) performing discharge molding on the product in step (a) to obtain anelectromagnetic shielding composite.

The present inventors have endeavored to develop a composite with anexcellent electromagnetic shielding performance. As a result ofmanufacturing a molded product by mixing copper- and nickel-platedcarbon fibers obtained by continuous electroless and electrolyticprocesses and a thermoplastic resin or a thermosetting resin, and thenperforming injection, extrusion, or discharge molding on the mixture, anexcellent electromagnetic shielding effect as well as superioreconomical feasibility and productivity was confirmed.

In the present invention, an electromagnetic shielding composite isprepared by mixing (i) (i-1) a thermoplastic resin or (i-2) athermosetting resin, and (ii) copper- and nickel-plated carbon fibersobtained by continuous electroless and electrolytic processes, andperforming molding on the mixture.

Hereinafter, the method of the present invention for preparing anelectromagnetic shielding composite will be described by steps indetail.

According to an aspect of the present invention, the method forpreparing an electromagnetic shielding composite using a thermoplasticresin is as follows:

(a) Mixing Thermoplastic Resin and Copper- and Nickel-Plated CarbonFibers

First, the method of the present invention includes a step of mixing50-90 wt % of a thermoplastic resin and 10-50 wt % of a copper- andnickel-plated carbon nanotube obtained by continuous electroless andelectrolytic processes.

According to an embodiment of the present invention, the thermoplasticresin is dried using various dryers known in the art, for example, ahot-air dryer, before use.

The thermoplastic resin used in the present invention forms a matrix,and if the content thereof is less than 50 wt %, the moldability andphysical properties may be degraded, and if the content thereof is morethan 90 wt %, the volume resistance and electromagnetic shieldingperformance may deteriorate.

According to another embodiment of the present invention, the mixture instep (a) contains 70-90 wt % of a thermoplastic resin and 10-30 wt % ofcopper- and nickel-plated carbon fibers, and more preferably, 70-80 wt %of a thermoplastic resin and 20-30 wt % of copper- and nickel-platedcarbon fibers.

The thermoplastic resin used in the present invention may includevarious thermoplastic resins known in the art, and may be preferably atleast one thermoplastic resin selected from the group consisting ofpolycarbonate-based resins, polystyrene-based resins, polyether-basedresins, polysulfone-based resins, polyolefin-based resins,polyimide-based resins, fluorine-based resins, poly(meth)acrylate-basedresins, polyacetal-based resins, polyamide-based resins, aromaticvinyl-based resins, acrylic-butadiene-styrene copolymer resins, andpolyvinylchloride-based resins, more preferably at least one selectedfrom the group consisting of polypropylene (PP), polyamide 6 (PA6),polycarbonate (PC), and acrylonitrile-butadiene-styrene resin (ABS), andstill more preferably PP, PA6, PC, PC and ABS, or ABS.

The carbon fibers used in the present invention may include variouscarbon fibers known in the art, and may be commercially purchased, orone prepared from PAN-based or pitch-based materials may be used.

Meanwhile, highly conductive carbon fibers can be obtained by platingcarbon fibers with metals, and the average diameter of the highlyconductive carbon fibers is 7 μm, and 7.25 μm to 9.5 μm in cases ofincluding the plating thickness, but the diameter of the fibers is notparticularly limited to the range of the present invention.

In addition, the carbon fibers used for plating are a bundle type of12,000 TEX, but the size of TEX is not limited.

The prepared highly conducive carbon fibers may be processed in achopped state, as shown in FIG. 4, in order to improve processabilityand dispersibility with a resin.

If the content of the copper- and nickel-plated carbon fibers used inthe present invention is less than 10 wt %, the electromagneticshielding performance may deteriorate, and if the content thereof ismore than 50 wt %, physical properties of the composite may be degraded,and the processability and economical feasibility may deteriorate.

According to still another embodiment of the present invention, thecopper- and nickel-plated carbon fibers in step (a) have a chopped shapewith a length of 3 mm to 500 mm.

According to another embodiment of the present invention, the product instep (a) further contains a conductive material selected from the groupconsisting of ferrite, graphite, and metal-plated graphite.

The conductive material may be contained in the electromagneticshielding composite of the present invention for the purpose of reducingthe surface resistance and enhancing the internal conductivity of thecomposite.

In cases where the conductive material is contained, the product in step(a) contains preferably 40-89.5 wt % of a thermoplastic resin, 10-50 wt% of copper- and nickel-plated carbon fibers, and 0.5-10 wt % of aconductive material, more preferably 67-89 wt % of a thermoplasticresin, 10-30 wt % of copper- and nickel-plated carbon fibers, and 1-3 wt% of a conductive material.

According to still another embodiment, the metal which is plated on thegraphite is at least one metal selected from the group consisting ofaluminum, iron, chromium, stainless steel, copper, nickel, black nickel,silver, gold, platinum, palladium, tin, cobalt, and an alloy of two ormore thereof, more preferably at least one metal selected from the groupconsisting of aluminum, chromium, copper, nickel, silver, platinum,palladium, tin, cobalt, and an alloy of two or more thereof, still morepreferably copper, nickel, palladium, or tin, and most preferablynickel.

According to another embodiment of the present invention, the mixing instep (a) is performed by further containing at least one additiveselected from the group consisting of a carbon filler, a flameretardant, a plasticizer, a coupling agent, a heat stabilizer, a lightstabilizer, an inorganic filler, a releasing agent, a dispersing agent,an anti-dropping agent, and a weathering stabilizer.

According to still another embodiment of the present invention, themethod of the present invention further includes, between steps (a) and(b), (a-1) preparing compounding pellets from the product in step (a)using an extruder for pellet manufacturing.

(a-1) Manufacturing Compounding Pellets

According to still another embodiment of the present invention, thecompounding pellets are manufactured using an extruder in conditions ofa temperature of 230-255° C. and a speed of 70-150 rpm.

As for the extruder, various extruders for pellet manufacturing that areknown in the art may be used. As for the extrusion conditions, thetemperature section of the extruder is divided into five, which are setto 230° C., 245° C., 245° C., 245° C., and 255° C., respectively, and aspeed of 80-120 rpm is more preferable.

(b) Performing Injection or Extrusion Molding, and ObtainingElectromagnetic Shielding Composite

Then, the method of the present invention includes a step of performinginjection or extrusion molding on the product in step (a) to obtain anelectromagnetic shielding composite.

In cases where the injection molding is adopted for the molding methodof the present invention, the injection molding in step (b) is performedusing an extruder preferably in conditions of a temperature of 215-275°C., a speed of 40-70 rpm, a pressure of 40-80 bars, and a mold coolingtime of 4-12 seconds, and more preferably in conditions of a speed of50-60 rpm, a pressure of 50-70 bars, and a mold cooling time of 6-10seconds while the temperature section of the extruder is divided intofive sections, which are set to 215-255° C., 220-265° C., 220-265° C.,220-265° C., and 230-275° C.

As the extruder used in the injection molding, various extruders thatare known in the art may be used.

In cases where the electromagnetic shielding composite is prepared bythe injection molding, the copper- and nickel-plated carbon fibers instep (a) have preferably a chopped shape with a length 3 mm to 20 mm,more preferably a chopped shape with a length of 3 mm to 12 mm, stillmore preferably a chopped shape with a length of 3 mm to 9 mm, stillmore preferably a chopped shape with a length of 5 mm to 7 mm, inconsideration of the size of a discharge port and the injectionpressure.

Meanwhile, in cases where the extrusion molding is adopted for themolding method of the present invention, the extrusion molding in step(b) is performed preferably using an extruder in conditions of atemperature of 230-265° C. and a speed of 30-60 rpm, and more preferablyusing a T-dice in conditions of a speed of 40-50 rpm while thetemperature section of the extruder is divided into five sections, whichare set to 230° C., 255° C., 255° C., 255° C., and 265° C.

As the extruder used in the injection molding, various extruders thatare known in the art may be used.

In cases where the electromagnetic shielding composite is prepared bythe injection molding, the electromagnetic shielding composite isprepared into a film or sheet form, and thus the copper- andnickel-plated carbon fibers in step (a) have preferably a chopped shapewith a length of 3 mm to 30 mm, more preferably a chopped shape with alength of 6 mm to 18 mm, and still more preferably a chopped shape witha length of 9 mm to 15 mm.

Through this method, the electromagnetic shielding composite may beprepared by mixing (i) a thermoplastic resin and (ii) copper- andnickel-plated carbon fibers obtained by continuous electroless andelectrolytic processes and then performing molding on the mixture.

According to another aspect of the present invention, the method forpreparing an electromagnetic shielding composite using a thermosettingresin is as follows:

The overlapping descriptions between the method for preparing anelectromagnetic shielding composite using a thermoplastic resin and themethod for preparing an electromagnetic shielding composite using athermosetting resin, for example, an additive such as a carbon filler,and the like, will be omitted in order to avoid excessive complicationof the present specification.

(a) Mixing Thermosetting Resin and Copper- and Nickel-Plated CarbonFibers

First, the method of the present invention includes a step of mixing50-90 wt % of a thermosetting resin and 10-50 wt % of copper- andnickel-plated carbon fibers obtained by continuous electroless andelectrolytic processes.

According to an embodiment of the present invention, the mixture in step(a) contains 70-90 wt % of a thermosetting resin and 10-30 wt % ofcopper- and nickel-plated carbon fibers, and more preferably, 75-88 wt %of a thermoplastic resin and 15-25 wt % of copper- and nickel-platedcarbon fibers.

For the thermosetting resin used in the present invention, variousthermosetting resins that are known in the art are used, and a liquidphase is used due to characteristics of the resin. The thermosettingresin is at least one thermosetting resin selected from the groupconsisting of polyurethane-based resins, epoxy-based resins,phenol-based resins, urea-based resins, melamine resins, and unsaturatedpolyester-based resins, and the thermosetting resin is more preferably apolyurethane-based resin, an epoxy-based resin, or a phenol-based resin,and still more preferably, a polyurethane resin or an epoxy resin.

In cases of using the thermosetting resin, a copper- and nickel-platedcarbon nanofiber in a chopped shape with a length of 3 mm to 500 mm maybe used, and a copper- and nickel-plated carbon nanofiber in a choppedshape with a length of 3 mm to 60 mm is more preferable.

In cases where a polyurethane resin is used as the thermosetting resinwithin the above range, the copper- and nickel-plated carbon fibers havepreferably a chopped shape with a length of 3 mm to 20 mm, morepreferably a chopped shape with a length of 3 mm to 9 mm, and still morepreferably a chopped shape with a length of 5 mm to 7 mm. Meanwhile, incases where an epoxy resin is used as the thermosetting resin, the epoxyresin and a setting agent (preferably, acid anhydride base) are mixed ata weight ratio of 1:0.8-0.96, and then the mixture is mixed with copper-and nickel-plated carbon fibers. Here, the copper- and nickel-platedcarbon fibers have preferably a chopped shape with a length of 3 mm to30 mm, more preferably a chopped shape with a length of 6 mm to 18 mm,and still more preferably a chopped shape with a length of 9 mm to 15mm.

The mixing may be performed using various mixers that are known in theart for dispersibility of the carbon fibers in the thermosetting resin,preferably at a speed of 500-1500 for 30-5 minutes.

According to still another embodiment of the present invention, theproduct in step (a) further contains a conductive material selected fromthe group consisting of ferrite, graphite, and metal-plated graphite,and more preferably, the product in step (a) contains 40-89.5 wt % of athermosetting resin, 10-50 wt % of copper- and nickel-plated carbonfibers, and 0.5-10 wt % of a conductive material.

(b) Performing Discharge Molding, and Obtaining ElectromagneticShielding Composite

Then, the method of the present invention includes a step of performingdischarge molding on the product in step (a) to obtain anelectromagnetic shielding composite.

According another embodiment of the present invention, the dischargemolding in step (b) further includes: (b-1) discharging the product instep (b) into a mold or a conveyor; (b-2) setting the discharged productin step (b-1); and (b-3) releasing the set product in step (b-2).

In step (b-1), the mold is preferably subjected to release treatment,before the mixture liquid of the thermosetting resin and the copper- andnickel-plated carbon fiber, which is the product in step (b), isdischarged into the mold or the conveyor. The release treatment may beperformed using various releasing agents that are known in the art.

According to a still more embodiment of the present invention, thesetting in step (b-2) may be performed by applying heat, pressure, orUV.

Through this method, the electromagnetic shielding composite may beprepared by mixing (i) a thermosetting resin and (ii) copper- andnickel-plated carbon fibers obtained by continuous electroless andelectrolytic processes and then performing molding on the mixture.

According to still another aspect of the present invention, there isprovided a method for preparing an electromagnetic shielding composite,the method including: (a) putting a copper- and nickel-plated carbonfiber obtained by continuous electroless and electrolytic processes intoa mold or a conveyor; and (b) putting a thermosetting resin to thecarbon fibers in step (a) to immerse the carbon fibers in thethermosetting resin, thereby obtaining an electromagnetic shieldingcomposite.

According to the method, a molded product may be manufactured by firstarranging highly conductive carbon fibers with a length of 30 mm to 60mm on a flat mold or a mold and discharging the thermosetting resinthereinto.

The electromagnetic shielding composite prepared through the moldingprocedure can obtain a low surface resistance and excellentelectromagnetic shielding property since the carbon fibers are dispersedto form multiple contact points in the molded product, such that thecarbon fibers are dispersed in a network form in which the carbon fibersare linked to each other.

It can be verified from FIG. 3 that the highly conductive carbon fibersare dispersed in a network form in the resin.

One of the greatest characteristics of the present invention is that theelectromagnetic shielding composite prepared by the method of thepresent invention contains copper- and nickel-plated carbon fibersobtained by continuous electroless and electrolytic processes, and thushas a further improved electromagnetic shielding effect compared withthe non-plated carbon fibers.

The copper- and nickel-plated carbon fibers used in the presentinvention are highly conductive carbon fibers with excellent electricalconductivity obtained by continuous electroless and electrolyticprocesses, which have been developed by the present inventors, and areprepared by the method as follows.

Specifically, the copper- and nickel-plated carbon fibers obtained bycontinuous electroless and electrolytic processes are prepared by themethod including the following steps: (a) allowing carbon fibers to passthrough an electroless plating liquid to plate the carbon fibers withcopper for 6-10 minutes, the electroless plating liquid containing, onthe basis of the volume of pure water, 2.5-5.5 g/l Cu ions, 20-55 g/lEDTA, 2.5-4.5 g/l formalin, 2-6 g/l triethanolamine (TEA), 25% NaOH 8-12ml/1, and 0.008-0.15 g/l 2,2′-bipiridine, at pH 12-13 and a temperatureof 36-45° C.; and (b) allowing the copper-plated carbon fiber in step(a) to pass through an electrolytic plating liquid to plate thecopper-plated carbon fiber with nickel for 1-3 minutes, the electrolyticplating liquid containing 280-320 g/l Ni(NH₂SO₃)₂, 15-25 g/l NiCl₂, and35-45 g/l H₃BO₃, at pH 4.0-4.2 and a temperature of 50-60° C.

Hereinafter, the method of the present invention for preparingmetal-plated carbon fibers obtained by continuous electroless andelectrolytic processes will be described by the following steps:

(a) Electroless Plating Process

First, the method of the present invention includes a step ofelectroless plating carbon fibers with a metal.

In one embodiment, in cases where the carbon fibers are plated withcopper, an electroless plating liquid contains pure water, a coppermetal salt, a complexing agent, a reducing agent, a stabilizer, and a pHadjusting agent.

The copper metal salt contained in the electroless plating liquidsupplies copper ions to impart conductivity to the carbon fibers, andformalin as a reducing agent, EDTA as a complexing agent,triethanolamine (TEA) and 2,2′-bipiridine as a stabilizer, and 25% NaOHas a pH adjusting agent were used.

As can be confirmed in examples, the more the contents of formalin as areducing agent and NaOH as a pH adjusting agent, which are contained inthe electroless plating liquid, the faster the plating rate, but theshorter the lifespan of the plating liquid, and thus considering thismatter, the contents of the reducing agent and the pH adjusting agentwere adopted.

Meanwhile, as can be clearly confirmed from examples, as a result oftesting the plating rate and the liquid stability by adjusting thecontent of the reducing agent while the contents of the copper ions andthe complexing agent increase at the same ratio, the plating rate andthe thickness of the plating layer can be controlled by adjusting theconcentrations of copper ions and formalin as a reducing agent, and thespecific gravity, strength, elastic modulus, and strain can becontrolled through the control of the thickness of the plating layer.However, since a thicker plating layer results in the increase in thespecific gravity and the deteriorations in the strength, elasticmodulus, and strain, the present invention solved the above problems byconducting electrolytic plating while the concentrations of the copperions and formalin as a reducing agent were adjusted, thereby improvingconductivity with a thin thickness. This is why the present inventionadopts continuous electroless and electrolytic processes.

According to another embodiment of the present invention, theelectroless plating step in step (a) is characterized by allowing carbonfibers to pass through an electroless plating liquid to plate the carbonfibers with copper for 6-10 minutes, the electroless plating liquidcontaining, on the basis of the volume of pure water, 2.5-3.5 g/l Cuions, 25-35 g/l EDTA, 2.5-3.5 g/l formalin, 2-3 g/l triethanolamine(TEA), 25% NaOH 8-12 ml/1, and 0.008-0.01 g/l 2,2′-bipiridine, at pH12-13 and a temperature of 36-40° C.

According to still another embodiment of the present invention, theelectroless plating step in step (a) is characterized by allowing carbonfibers to pass through an electroless plating liquid to plate the carbonfibers with copper for 6-10 minutes, the electroless plating liquidcontaining, on the basis of the volume of pure water, 2.5-3.5 g/l Cuions, 20-30 g/l EDTA, 2.5-3.5 g/l formalin, 2-3 g/l triethanolamine(TEA), 25% NaOH 8-12 ml/l, and 0.008-0.01 g/l 2,2′-bipiridine, at pH12-13 and a temperature of 36-45° C.

According to another embodiment of the present invention, theelectroless plating step in step (a) is characterized by allowing carbonfibers to pass through an electroless plating liquid to plate the carbonfibers with copper for 6-10 minutes, the electroless plating liquidcontaining, on the basis of the volume of pure water, 4.5-5.5 g/l Cuions, 30-40 g/l EDTA, 2.5-3.5 g/l formalin, 4-6 g/l triethanolamine(TEA), 25% NaOH 8-12 ml/1, and 0.01-0.15 g/l 2,2′-bipiridine, at pH12-13 and a temperature of 40-45° C.

According to a high-rate plating bath in still another embodiment of thepresent invention, the electroless plating in step (a) is characterizedby allowing carbon fibers to pass through an electroless plating liquidto plate the carbon fibers with copper for 6-10 minutes, the electrolessplating liquid containing, on the basis of the volume of pure water,4.5-5.5 g/l Cu ions, 45-55 g/l EDTA, 3.5-4.5 g/l formalin, 4-6 g/ltriethanolamine (TEA), 25% NaOH 8-12 ml/1, and 0.01-0.15 g/l2,2′-bipiridine, at pH 12-13 and a temperature of 40-45° C.

In addition, after the electroless plating, three stages of washing wereperformed, and the third washing among the three stages of washing wasperformed by adding 1-2% H₂SO₄. This is for keeping the pH of anelectrolytic plating bath and activating surfaces of theelectroless-plated carbon fibers.

(b) Electrolytic Plating Process

Next, the method of the present invention includes a step of, after thecarbon fibers are plated with copper by the electroless plating process,continuously plating the carbon nanotubes with nickel by an electrolyticplating process.

One of the characteristics of the present invention is that theelectrical conductivity of the carbon fibers was improved by conductingan electroless plating process and then a nickel electrolytic platingprocess.

An electrolytic plating liquid for conducting the electrolytic platingprocess employs Ni(NH₂SO₃)₂ and NiCl₂ as a nickel metal salt and H₃BO₃as a pH buffer.

As can be clearly confirmed from examples, the carbon fibers obtained bycontinuous electroless and electrolytic processes reduced the electricresistance value by about 32-to 37-fold compared with non-plated carbonfibers, and reduced by 2-fold compared with comparative examples,thereby improving electrical conductivity.

It is determined that the copper pores are filled by quickly conductingthe Ni electrolytic plating, after the electroless plating, and as aresult, the electrical conductivity was improved.

According to another embodiment of the present invention, theelectrolytic plating process in step (b) is performed by applying aconstant voltage (CV) of 5-15 V.

In cases of the electroless copper plating and electrolytic nickelplating continuous processes, the electrolytic plating process isperformed by applying a constant voltage (CV) of 5-10 V, and morepreferably 6-8 V.

The advantage of the electroless and electrolytic plating is that analloy layer is formed that exhibits excellent electrical conductivity,is effective in adhesive strength and flexibility, has a thin thicknessdue to an electrolytic metal material adhering to spaces of the metal,which are generated in the electroless plating, and retains excellentconductivity. In addition, the electroless and electrolytic platingproduces an effect of uniformly plating carbon fibers.

Electroless (copper) plating is first performed, and electrolyticplating was continuously performed. A voltage is applied to carbonfibers put in the bath, and thus electrolyte ions are combined withpores generated from the electroless plating, thereby producing aproduct with a small plating thickness and improved conductivity.

According to still another embodiment of the present invention, thecarbon fibers in step (a) are pre-treated by the method including thefollowing steps: (i) allowing carbon fibers to pass through an aqueoussolution containing a surfactant, an organic solvent, and a non-ionicsurfactant, to degrease and soften the carbon fibers; (ii) allowing thecarbon fibers resulting from step (i) to pass through an aqueoussolution containing sodium bisulfate (NaHSO₃), H₂SO₄, ammoniumpersulfate ((NH₄)₂S₂O₈), and pure water, to conduct an etching processthat functions neutralizing, washing, and conditioning; (iii) allowingthe carbon fibers resulting from step (ii) to pass through an aqueoussolution of PdCl₂ to conduct a sensitizing process; and (iv) allowingthe carbon fibers resulting from step (iii) to pass through an aqueoussolution of sulfuric acid (H₂SO₄) to conduct an activating process.

(i) Degreasing and Softening Carbon Fibers

In the method of the present invention, for the pretreatment of thecarbon fibers, first, the carbon fibers are degreased and softened byallowing the carbon fibers to pass through an aqueous solutioncontaining a surfactant, an organic solvent, and a non-ionic surfactant.

The aqueous solution containing a surfactant, an organic solvent, and anon-ionic surfactant performs a degreasing action of removing epoxy orurethane that has been sized to the carbon fibers while swelling tosoften the surfaces of the fibers.

According to still another embodiment of the present invention, theaqueous solution in step (i) contains 15-35 wt % of a solution, as asurfactant, in which pure water and NaOH are mixed at a weight ratio of40-49:1-10, 50-80 wt % of diethyl propanediol and 5-15 wt % ofdipropylene glycol methyl ether as an organic solvent, and a non-ionicsurfactant with 400-600 ppm, and more preferably, 20-30 wt % of asolution, as a surfactant, in which pure water and NaOH are mixed at aweight ratio of 45-48:2-5, 58-72 wt % of diethyl propanediol and 8-12 wt% of dipropylene glycol methyl ether as an organic solvent, and anon-ionic surfactant with 400-600 ppm.

The non-ionic surfactant may include various non-ionic surfactants inthe art, preferably includes ethoxylated linear alcohol, ethoxylatedlinear alkyl-phenol or ethoxylated linear thiol), more preferably isethoxylated linear alcohol.

According to still another preferable embodiment of the presentinvention, step (i) was performed at a temperature of 40-60° C. for 1-5minutes, and more preferably at a temperature of 45-55° C. for 1-3minutes.

(ii) Etching Process

Next, for the pretreatment of the carbon fibers, an etching process isperformed that neutralizes strong alkali components, helps a washingprocess for a next process, a sensitizing process, and performs aconditioning action.

An aqueous solution for the etching process contains sodium bisulfate(NaHSO₃), sulfuric acid (H₂SO₄), ammonium persulfate ((NH₄)₂S₂O₈), andpure water.

More preferably, the aqueous solution in step (ii) contains 0.1-10 wt %of sodium bisulfate (NaHSO₃), 0.1-3 wt % of sulfuric acid (H₂SO₄), 5-25wt % of ammonium persulfate ((NH₄)₂S₂O₈), and 62-94.8 wt % of purewater, and still more preferably, 0.8-2 wt % of sodium bisulfite;NaHSO₃, 0.3-1 wt % of sulfuric acid (H₂SO₄), 10-20 wt % of ammoniumpersulfate ((NH₄)₂S₂O₈), and 77-88.9 wt % of pure water.

According to still another preferable embodiment of the presentinvention, step (ii) is performed at a temperature of 20-25° C. for 1-5minutes, and more preferably at a temperature of 20-25° C. for 1-3minutes.

(iii) Sensitizing Process

Then, a sensitizing process is performed by allowing the carbon fibersresulting from step (ii) to pass through an aqueous solution of PdCl₂.

The sensitizing process is for allowing metal ions to be adsorbed on thesurfaces of the surface-modified carbon fibers.

The concentration of the aqueous solution of PdCl₂ is more preferably10-30%, and still more preferably 15-25%.

According to still another embodiment of the present invention, step(iii) was performed at a temperature of 20-40° C. for 1-5 minutes, andmore preferably at a temperature of 25-35° C. for 1-3 minutes.

(iv) Activating Process

Then, for the pretreatment method of the carbon fibers, an activatingprocess is performed by allowing the carbon fibers resulting from step(iii) to pass through an aqueous solution of sulfuric acid (H₂SO₄).

The activating process is shown to be performed after the sensitizingprocess in the present description, but conducting the activatingprocess together with the sensitizing process is included within thescope of the present invention.

The activating process is performed in order to remove Sn that has beencolloidized for the prevention of Pd oxidation.

More preferably, the concentration of the aqueous solution of sulfuricacid (H₂SO₄) is 5-15%.

According to still another preferable embodiment of the presentinvention, step (iv) is performed at a temperature of 40-60° C. for 1-5minutes, and more preferably at a temperature of 45-55° C. for 1-3minutes.

The carbon fibers may be pre-treated by this method, and the pre-treatedcarbon fibers may be plated with metals, copper and nickel, bycontinuous electroless and electrolytic processes.

According to still another aspect of the present invention, the presentinvention provides an electromagnetic shielding composite prepared bythe method of the present invention.

The electromagnetic shielding composite of the present invention isprepared by the preparation method of the electromagnetic shieldingcomposite, and thus the overlapping descriptions therebetween areomitted to avoid excessive complication of the specification due torepetitive descriptions thereof.

The electromagnetic shielding composite of the present invention can beused for electromagnetic shielding by being inserted into a hand phonecover and a pouch, and can be applied to brackets for protecting LCD,which is a portable display product.

Advantageous Effects

Features and advantages of the present invention are summarized asfollows.

(a) The present invention provides a method for preparing anelectromagnetic shielding composite and an electromagnetic shieldingcomposite prepared by the method.

(b) The present invention can provide an electromagnetic shieldingcomposite which is suitable for EMI shielding due to excellentconductivity and a low surface resistance thereof, and has excellentproductivity and economical feasibility, by using highly conducivecarbon fibers obtained by continuous electroless and electrolyticprocesses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a process for preparing anelectromagnetic shielding composite according to an embodiment of thepresent invention.

FIG. 2 is a cross-sectional image of a highly conductive carbon fiberplated by continuous electroless and electrolytic processes.

FIG. 3 is an image showing a surface in which highly conductive carbonfibers in a chopped shape are dispersed in a network form with contactpoints.

FIG. 4 is an image showing that highly conductive carbon fibers platedby continuous electroless and electrolytic processes are processed in achopped shape.

FIG. 5 is a graph showing an electromagnetic shielding effect of amolded product using carbon fibers prepared by the continuous processes.

FIG. 6 is a view showing a sample for the electromagnetic shieldingtest.

FIG. 7 is a block diagram showing a process for preparing anelectromagnetic shielding composite using a thermosetting resinaccording to another embodiment of the present invention.

FIG. 8 shows an apparatus for surface treatment of carbon fibers, usedin the present invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail withreference to examples. These examples are only for illustrating thepresent invention more specifically, and it will be apparent to thoseskilled in the art that the scope of the present invention is notlimited by these examples.

Throughout the present specification, the term “%” used to express theconcentration of a specific material, unless otherwise particularlystated, refers to (wt/wt) % for solid/solid, (wt/vol) % forsolid/liquid, and (vol/vol) % for liquid/liquid.

EXAMPLES Materials and Methods

The respective components used in examples and comparative examples wereas follows:

(A) As a thermoplastic resin, BJ700 from Samsung Total was used forpolypropylene (PP), KN120 from Kolon was used for polyimide 6 (PA6),LUPOY PC1201-22 from LG Chemical was used for polycarbonate (PCT), andABS XR401 from LG Chemical was used for anacrylonitrile-butadiene-styrene (ABS) resin. (B) As a thermosettingresin, UP 395 from Kukdo Chemical was used for polyurethane (PU), andKBR1753 from Kukdo Chemical was used for epoxy. In addition, (C) ascarbon fibers, Cu—Ni-plated carbon fibers through continuous electrolessand electrolytic processes, which were prepared by Bulsone Material wereused. The carbon fibers were cut into chopped shapes with 6 mm, 12 mm,and 30 mm. In addition, as other additives, a product from Novamet wasused for nickel-plated graphite.

Meanwhile, the electromagnetic shielding test, that is, EMI shieldingproperty (dB) was determined by measuring the electromagnetic shieldingperformance according to ASTM D 4935.

Example 1: Manufacturing of Electromagnetic Shielding Sheets byInjection Molding and Evaluation Thereof

Molding was performed while the contents of the respective componentswere shown in table 1. Injection molded products were manufactured in asheet form with a thickness of 0.7 mm. Specifically, thermoplasticresins, PP (grade BJ 700, melting index: 25, density: 0.91 g/cm³, heatdeflection temperature: 105° C., Samsung Total), PC (grade LUPOY PC1201-22, melting index: 22, density: 1.2 g/cm³, heat deflectiontemperature: 147° C., LG Chemical), and ABS (grade ABS XR401, meltingindex: 9, density: 1.05 g/cm³, heat deflection temperature: 105° C., LGChemical) were, respectively, dried for 6 hours in a vacuum oven at 80°C. After that, the dried thermoplastic resins were mixed in contentsthereof shown in table 1. Then, each mixture was fed into an extruder(twin injection machine; manufactured by Woojin, Korea, GT-1 9300), andinjected through a mold with a standard specified by ASTM D4935. Incases of the PP mixture, the temperature section was divided into five,which was set to 215° C., 220° C., 220° C., 220° C., and 230° C.,respectively, and working was performed under 55 rpm, 60 bars, and amold cooling time of 8 seconds. In cases of the PC mixture and the ABSmixture, the temperature was set to 255° C., 265° C., 265° C., 265° C.,and 275° C. in the same machine, and working was performed under 55 rpm,60 bars, and a mold cooling time of 8 seconds.

The manufactured sheets were subjected to an electromagnetic shieldingtest, and the result values are shown (table 1).

TABLE 1 Highly EMI SE conductive Thermoplastic (dB) (at carbon fibersAdditive resin 1.0 GHz) Cu + Ni — PP 70 wt % 72 carbon fibers Ferrite 2wt % PP 68 wt % 72 (6 mm, Ni-plated graphite 2 wt % PP 68 wt % 82 30 wt%) — PC 70 wt % 67 Ferrite 2 wt % PC 68 wt % 70 Ni-plated graphite 2 wt% PC 68 wt % 81 — PC/ABS 70 wt % 68 Ferrite 2 wt % PC/ABS 68 wt % 72Ni-plated graphite 2 wt % PC/ABS 68 wt % 81 — PA6 70 wt % 81 Ferrite 2wt % PA6 68 wt % 80 Ni-plated graphite 2 wt % PA6 68 wt % 84

Example 2: Manufacturing of Molded Products by Injection and ExtrusionMolding Processes and Evaluation Thereof

Molded products were manufactured from the above components by injectionand extrusion processes shown in tables 2 and 3, respectively, and theelectromagnetic shielding performance thereof was tested. For themanufacturing of the injection molded products shown in table 2 below,PP (grade BJ 700, melting index: 25, density: 0.91 g/cm³, heatdeflection temperature: 105° C., Samsung Total) was dried in a vacuumoven at 80° C. for 6 hours. Then, the dried PP was mixed with copper-and nickel-plated carbon fibers (6 mm) in contents thereof shown intable 2 below. In addition, sheets were manufactured by injecting themixtures into injected products with a size specified by ASTM D4935 inthe same conditions as in example 1.

TABLE 2 Manufacturing of molded product through injection molding EMI SE(dB) Composite (at 1.0 GHz) PP/Cu—Ni carbon fibers (90/10 wt %) 16.4PP/Cu—Ni carbon fibers (80/20 wt %) 54 PP/Cu—Ni carbon fibers (70/30 wt%) 72 Injection molding, fiber length 6 mm chopped

Meanwhile, for the manufacturing of the extrusion molded products shownin table 3 below, PA6 (KOPA KN120, melting point: 222° C., density: 1.14g/cm³, relative viscosity (RV): 2.75, KOLON Ltd) was dried for 6 hoursin a vacuum oven at 80° C. The dried PA6 was mixed with copper- andnickel-plated carbon fibers (12 mm) in contents thereof shown in table 3below. In addition, the mixtures were fed into an extruder for pelletmanufacturing (twin screw compounding extruder; Bowtech, Korea, BA-11)while the temperature section was divided into five, which was set to230° C., 245° C., 245° C., 245° C., and 255° C., respectively, and thendischarged at 100 rpm, followed by a water cooling process, therebymanufacturing composite pellets. The manufactured pellets were made intosheet form molded products with a thickness of 0.7 mm, using T-dice inan extruder for sheet manufacturing, self-manufactured by Ecogreen attemperature sections of 230° C., 255° C., 255° C., 255° C., and 265° C.,at a speed of 45 rpm.

TABLE 3 Manufacturing of molded product through extrusion molding EMI SE(dB) Composite (at 1.0 GHz) PA 6/Cu—Ni carbon fibers (90/10 wt %) 25.4PA 6/Cu—Ni carbon fibers (80/20 wt %) 58.2 PA 6/Cu—Ni carbon fibers(70/30 wt %) 81 Extrusion molding, fiber length 12 mm chopped

Example 3: Manufacturing Molded Products Using Thermosetting Resins andEvaluation Thereof

In table 4, sheets were manufactured by immersing highly conductive Cu-and Ni-plated carbon fibers in a polyurethane resin and an epoxy resin,which are representative thermosetting resins, and the electromagneticshielding performance thereof was measured.

Polyurethane PU (grade UP 395, viscosity: 1500 cps, specific gravity: 1,one-component urethane, Korea, Kukdo Chemical) and copper- andnickel-plated carbon fibers (6 mm chop) were quantified at a weightratio of 80:20 in a beaker, and then mixed at 1000 rpm in a mixer for 1minute, thereby preparing a mixture liquid. 20 g of the prepared mixtureliquid was drawn off on a glass substrate that was subjected to releasetreatment (an appropriate amount of WD-40 from 3M was sprayed on a 5mm-thick glass substrate, which was then uniformly rubbed with a cottoncloth, and then kept in an oven at 70° C. for 3 minutes, therebyinducing the sufficient stabilization of the releasing agent, and thenthe surface is wiped with a smooth tissue, and the pollutants werefinally removed), and was pushed to have a thickness of 0.7 mm by aglass rod, thereby molding a sheet form. The molded glass substrate wasdried and hardened in an oven at 50° C. for 24 hr, thereby obtaining afinal molded product.

An epoxy resin (KBR-1753, viscosity: 800 cps, Korea, Kukdo Chemical) anda hardener (KBH-1089, Acid Anhydride-based, Korea, Kukdo Chemical) weremixed at a weight ratio of 100:92 to prepare a mixed epoxy solution. Themixed solution and the copper- and nickel-plated carbon fibers (12 mmchop) were quantified at a weight ratio of 80:20 in a beaker, and mixedin a mixer at 100 rpm for 1 minute, thereby preparing a mixture liquid.20 g of the prepared mixture liquid was drawn off on a glass substratethat was subjected to release treatment, and was pushed to have athickness of 0.7 mm by a glass rod, thereby molding a sheet form. Themolded glass substrate was dried and cured in an oven at 150° C. for 24hr, thereby obtaining a final molded product.

TABLE 4 EMI SE (dB) Composite (at 1.0 GHz) Polyurethane/Cu—Ni carbonfibers (80/20 wt %) (6 mm) 56.7 Mixed epoxy solution/Cu—Ni carbon fibers57.3 (80/20 wt %) (12 mm)

Comparative Example 1: Manufacturing of Injection and Extrusion MoldedProducts Using Non-Plated Carbon Fibers and Evaluation Thereof

In comparative example 1, the non-plated carbon fibers were subjected toinjection molding and extrusion molding, respectively, and the shieldingperformance thereof was measured. Specifically, the non-treated carbonfiber chops with a length of 6 mm or 12 mm were subjected to molding incontents thereof shown in table 5 under the same conditions as inexamples 1 and 2, thereby obtaining molded products. In cases of theextrusion molding, the pellets were first prepared, and dried in adrying furnace, and then manufactured into continuous type sheets with athickness of 0.7 mm in an extruder.

TABLE 5 EMI SE (dB) Composite (at 1.0 GHz) Molding method PP/carbonfibers (80/20 wt %) (6 mm) 13 Injection molding PA 6/carbon fibers(80/20 wt %) 14 Extrusion (12 mm) molding

It can be seen that, in examples 1, 2, and 3 above, the electromagneticshielding performance is different depending on the content of highlyconductive carbon fibers regardless of the kind of resin. In addition,when the nickel-coated graphite was added at the compositional ratio ofthe same content of the highly conductive carbon fibers, theelectromagnetic shielding effect slightly increased.

It seems that the reason why the shielding efficiency slightly increasedin the injection molding rather than in the extrusion molding is thatthe surface of the molded product has an integral skin due to the moldin cases of the extrusion molding.

The reason why example 3 had a slight increase in the shieldingefficiency compared with the extrusion molded product using thethermoplastic resin is that the mutual contact points between carbonfibers were formed more stably in example 3 rather than the injectionmolded product.

In comparative example 1, the injection and extrusion molded productsusing the metal-non-plated carbon fibers showed a half level of theelectromagnetic shielding efficiency compared with the same content ofthe highly conductive carbon fibers.

Therefore, the present invention shows that the electromagneticshielding effect is very excellent when a predetermined content ofhighly conductive carbon fibers obtained by continuous electroless andelectrolytic processes are contained.

Meanwhile, the Cu—Ni double-plated carbon fibers obtained by continuouselectroless and electrolytic processes, which were manufactured byBulsone Material and used in examples 1 to 3 above, were pretreated andprepared through the following process.

Example 4: Pretreatment Procedure of Carbon Fibers

1) Degreasing and Softening Processes

First, the epoxy or urethane that has been sized to the carbon fiberswas removed using an organic solvent, and a process of swelling tosoften the surfaces of the fibers was performed at the same time.

The degreasing and softening processes were performed by allowing carbonfibers (12K, purchased from Toray, Hyosung, or Taekwang (TK)) to passthrough a pretreatment bath containing 25 wt % of a solution in whichpure water and NaOH were mixed at a weight ratio of 47:3, as asurfactant; 65 wt % of diethyl propanediol and 10 wt % of dipropyleneglycol methyl ether, as an organic solvent; and 500 ppm ethoxylatedlinear alcohol as a non-ionic surfactant (low foam). The degreasing andsoftening processes were performed at a temperature of 50° C. for 2minutes.

2) Etching Process

An etching process was performed, in order to neutralize strong alkalicomponents of NaOH using sulfuric acid (H₂SO₄), reducing the load of asensitizing process as a next process, and helping a washing action andperforming a conditioning action using ammonium peroxysulfate((NH₄)₂S₂O₈) to enhance the adsorption of palladium.

Specifically, an etching process was performed by allowing the carbonfibers, which were subjected to the degreasing and softening processes,to pass through a pretreatment bath containing 1 wt % of sodiumbisulfate (NaHSO₃), 0.5 wt % of sulfuric acid (H₂SO₄), 5 wt % ofammonium persulfate ((NH₄)₂S₂O₈), and 83.5 wt % of pure water, toperform neutralizing, washing, and conditioning actions. The etchingprocess was performed at a temperature of 20-25° C. for 2 minutes.

3) Sensitizing Process (Catalyst Imparting Process)

A sensitizing process was performed by treating the carbon fibers, whichwere subjected to the etching process, with 20% PdCl₂ at a temperatureof 30° C. for 2 minutes. The sensitizing process is performed in orderto allow metal ions to be adsorbed on surfaces of the surface-modifiedcarbon fibers.

4) Activating Process

An activating process is performed together with the sensitizingprocess. The carbon fibers were treated with 10% sulfuric acid (H₂SO₄)at a temperature of 50° C. for 2 minutes in order to remove Sn that hasbeen colloidized for the prevention of Pd oxidation.

The carbon fibers were pretreated by the above processes.

Examples 5 and 6: Copper- and Nickel-Plated Carbon Fibers Obtained byElectroless and Electrolytic Continuous Plating Processes

The carbon fibers (12K, purchased from Toray) pretreated in example 4and the carbon fibers (12K, purchased from Taekwang (TK)) pretreated inexample 4 were subjected to an electroless copper plating process in thecompositions and conditions shown in table 6, and then continuouslysubjected to an electrolytic nickel plating process in the compositionsand conditions shown in table 7, using a plating apparatus shown in theaccompanying FIG. 8, thereby preparing copper- and nickel-plated carbonfibers, which were then used for examples 5 and 6. Hereinafter, thecontents of components of the plating liquids are on the basis of 1 L ofpure water.

TABLE 6 Electroless copper plating iquid — Component Content(Conditions) Metal salt Cu ion 3 g/l Complexing agent EDTA 30 g/lReducing agent Formalin 3.0 g/l Stabilizer TEA (triethanol amine) 3 g/l

2,2′-bipiridine 0.01 g/l pH adjusting agent NaOH (25%) 12 ml/lTemperature 38° C. pH 12.5 Treatment time 6 min

TABLE 7 Electrolytic Ni plating liquid — Component Content (Conditions)Electrolytic Nickel metal salt Ni(NH₂SO₃)₂ 300 g/l plating liquid NiCl₂20 g/l pH buffer H₃BO₃ 40 g/l Temperature 55° C. pH 4.2 Treatment time 1min

Example 7: Copper- and Nickel-Plated Carbon Fibers Obtained byElectroless and Electrolytic Continuous Plating Processes

The carbon fibers pretreated in example 4 were subjected to anelectroless copper plating process in the compositions and conditionsshown in table 8, and then continuously subjected to an electrolyticnickel plating process in the compositions and conditions shown in table9, using a plating apparatus in the accompanying FIG. 8, therebypreparing copper- and nickel-plated carbon fibers.

TABLE 8 Electroless copper plating liquid — Component Content(Conditions) Metal salt Cu ion 2.5-3.5 g/l Complexing agent EDTA 25-35g/l Reducing agent Formalin 2.5-3.5 g/l Stabilizer TEA (triethanolamine) 2-3 g/l 2,2′-bipiridine 0.008-0.01 g/l pH adjusting agent NaOH(25%) 8-12 ml/l Temperature 36-40° C. pH 12-13 Treatment time 6-10 min

TABLE 9 Electrolytic Ni plating liquid — Component Content (Conditions)Electrolytic Nickel metal salt Ni(NH₂SO₃)₂ 280-320 g/l plating liqudNiCl₂ 15-25 g/l pH buffer H₃BO₃ 35-45 g/l Temperature 50-55° C. pH4.0-4.2 Treatment time 1-3 min

For the electrolytic plating, a constant voltage (CV) of 5-10 V wasapplied to an electrolytic nickel bath. A Ni metal plate or Ni ballswere used for a metal plate used as a positive electrode.

Example 8: Copper- and Nickel-Plated Carbon Fibers Obtained byElectroless and Electrolytic Continuous Plating Processes

The carbon fibers pretreated in example 4 were subjected to anelectroless copper plating process in the compositions and conditionsshown in table 10, and then continuously subjected to an electrolyticnickel plating process in the compositions and conditions shown in table11, using a plating apparatus in the accompanying FIG. 8, therebypreparing copper- and nickel-plated carbon fibers.

TABLE 10 Electroless copper plating liquid — Component Content(Conditions) Metal salt Cu ion 4.5-5.5 g/l Complexing agent EDTA 45-55g/l Reducing agent Formalin 3.5-4.5 g/l Stabilizer TEA (triethanolamine) 4-6 g/l 2,2′-bipiridine 0.01-0.15 g/l pH adjusting agent NaOH(25%) 8-12 ml/l Temperature 40-45° C. pH 12-13 Treatment time 6-10 min

TABLE 11 Electrolytic Ni plating liquid — Component Content (Conditions)Electrolytic Nickel metal salt Ni(NH₂SO₃)₂ 280-320 g/l plating liquidNiCl₂ 15-25 g/l pH buffer H₃BO₃ 35-45 g/l Temperature 50-55° C. pH4.0-4.2 Treatment time 1-3 min

For the electrolytic plating, a constant voltage (CV) of 5-10 V wasapplied to an electrolytic nickel bath. A Ni metal plate or Ni ballswere used for a metal plate used as a positive electrode.

Test Example 1: Measurement on Change in Current Density and LinearResistance Value of Plated Carbon Fiber

The optimization conditions for electroless and electrolytic platingwere set by adjusting the concentration of NaOH, which adjusts pH, andthe concentration of HCHO, which helps the reduction reaction of Cu,among the compositions and conditions for preparing copper- andnickel-plated carbon fibers in example 7.

While 25% NaOH varies 8, 9, 10, 11, and 12 ml/l, and HCHO varies 2.5,2.7, 2.9, 3.1, and 3.3 g/l, respectively, the change in the currentdensity (A) flowing through the carbon fibers was measured, and thelinear resistance (0/30 cm) of the finally obtained products (copper-and nickel-plated carbon fibers) was evaluated, and the results weresummarized in table 12 below. A constant voltage (CV) of 7 V was appliedto an electrolytic nickel bath, and the other conditions that wereuniformly maintained were summarized in tables 13 and 14 below.

TABLE 12 Resistance Period of use HCHO NaOH Current density (A) (Ω/30cm) of plating liquid 2.5 8 100 0.8 10 turns  9 110 0.6 10 120 0.4 11130 0.3 12 140 0.2 2.7 8 110 0.7 8 turns 9 120 0.6 10 130 0.5 11 140 0.312 150 0.2 2.9 8 120 0.6 6 turns 9 130 0.5 10 140 0.4 11 150 0.3 12 1600.2 3.1 8 130 0.6 4 turns 9 140 0.5 10 150 0.4 11 160 0.3 12 170 0.2 3.38 140 0.5 2 turns 9 150 0.4 10 160 0.3 11 170 0.2 12 180 0.1

In table 11 above, 1 turn expresses 1 make-up amount of electrolesscopper plating.

TABLE 13 Electroless copper plating liquid — Component Content(Conditions) Metal salt Cu ion 3 g/l Complexing agent EDTA 30 g/lReducing agent Formalin (HCHO) 2.5-3.3 g/l Stabilizer TEA (triethanolamine) 3 g/l 2,2′-bipiridine 0.10 g/l pH adjusting agent NaOH (25%) 8-12ml/l Temperature 37° C. pH 12.5 Treatment time 6 min

TABLE 14 Electrolytic plating liquid — Component Content (Conditions)Electrolytic Nickel metal salt Ni(NH₂SO₃)₂ 300 g/l plating liquid Nickelmetal salt NiCl₂ 20 g/l pH buffer H₃BO₃ 40 g/l Temperature 55° C. pH 4.2Treatment time 1 min Constant voltage (Cv) 7 V

As can be confirmed from table 12 above, as the amounts of the reducingagent and NaOH increased, the plating rate increased, but the lifespanof the plating liquid was shortened. Therefore, it may be preferable tomaintain the amount of the reducing agent at the minimum (2.5-3.0 g/l)and the amount of NaOH at the maximum.

Test Example 2: Test on Plating Rate and Liquid Stability

For the plating rate and the liquid stability test through theadjustment of the concentrations of copper ions and a complexing agent(EDTA), the optimization conditions for copper plating were tested byadjusting the amount of the reducing agent (table 15) when the copperions and the complexing agent were increased at the same ratio, and theother conditions that were uniformly maintained were summarized intables 16 and 17 below.

TABLE 15 Metal salt Reducing agent Complexing Plating thickness (Cu)(HCHO) agent (EDTA) NaOH (μm) 2.5 2.5 25 12 0.2-0.3 3.5 3.0 35 0.3-0.54.5 3.5 45 0.4-0.6 5.5 4 55 0.5-0.8

TABLE 16 Electroless copper plating liquid — Component Content(Conditions) Metal salt Cu ion 2.5-5.5 g/l Complexing agent EDTA 25-55g/l Reducing agent Formalin 2.5-4 g/l Stabilizer TEA (triethanol amine)3 g/l 2,2′-bipiridine 0.01 g/l pH adjusting agent NaOH (25%) 12 ml/lTemperature 37° C. pH 12.5 Treatment time 6 min

TABLE 17 Electrolytic plating liquid — Component Content (Conditions)Electrolytic Nickel metal salt Ni(NH₂SO₃)₂ 300 g/l plating liquid NiCl₂20 g/l pH buffer H₃BO₃ 40 g/l Temperature 55° C. pH 4.2 Treatment time 1min C.V 7 V

As can be seen from table 15 above, it was verified that, as theconcentrations of copper and HCHO were higher, the high-rate plating waspossible, and the thickness of the plating layer was increased (platingthickness: 0.7 microns or more). For a preferable plating thickness, 0.3μm, of the carbon fiber, the best products were obtained when theconcentration of copper ions was 2.5-3.0 g/l and the concentration ofHCHO was 2.5-3.0 g/l.

As the plating thickness of the carbon fiber increases, the specificgravity increases and the strength, elastic modulus, and straindeteriorate, and thus carbon fibers with excellent electricalconductivity were prepared by conducting Ni electrolytic plating on Cupores in a shorter time after the electroless plating, rather thancompulsorily increasing the plating thickness in the electrolessplating.

Test Example 3: Comparison of Physical Properties and ElectricalConductivity

Table 18 shows comparison of physical properties, electricalconductivity, and the like, between copper- and nickel-plated carbonfibers in examples 5 and 6 and nickel-plated carbon fibers on the marketprepared by an electroless plating process, as comparative example 2.

TABLE 18 Comparative — example 2 Example 5 Example 6 Note Strandstrength 280 380 338 — (kgf/mm²) (Range) (367~405) (325~353) Elasticmodulus (tons/mm²) 22.0 20.0 22.5 — Strain (%) 1.2 1.9 1.5 — Specificgravity (g/cm³) 2.70 2.7277 2.7894 — Diameter (μm) 7.5 7.828 7.705 — Tex1420 1575 1561 — (Fiber thickness) Electric resistance (Ω/m) — 0.8 0.7 —Electric resistance (Ωcm) 7.5 × 10⁻⁵ 4.62 × 10⁻⁵ 4.05 × 10⁻⁵ — Electricresistance compared — 32-fold 37-fold General with general CF reductionreduction CF: 1.50 × 10⁻³ Ωcm Coating thickness (nm) 250 240 350 —(210~271) (305~392)

As can be seen from table 18 above, the copper- and nickel-plated carbonfibers had excellent physical properties and exhibited excellentelectrical conductivity values due to the low electric conductivityvalues, compared with comparative example 2 prepared by the electrolessplating process.

Although the present invention has been described in detail withreference to the specific features, it will be apparent to those skilledin the art that this description is only for a preferred embodiment anddoes not limit the scope of the present invention. Thus, the substantialscope of the present invention will be defined by the appended claimsand equivalents thereof.

What is claimed is: 1.-20. (canceled)
 21. A method for preparing anelectromagnetic shielding composite comprising: (a) mixing 50-90 wt % ofa thermosetting resin and 10-50 wt % of copper- and nickel-plated carbonfibers obtained by continuous electroless and electrolytic processes;and (b) performing discharge molding on the product in step (a) toobtain an electromagnetic shielding composite.
 22. The method of claim21, wherein the thermosetting resin in step (a) is at least onethermosetting resin selected from the group consisting ofpolyurethane-based resins, epoxy-based resins, phenol-based resins, urearesins, melamine resins and unsaturated polyester-based resins.
 23. Themethod of claim 21, wherein the discharge molding in step (b) furthercomprises: (b-1) discharging the product in step (b) into a mold or aconveyor; (b-2) setting the discharged product in step (b-1); and (b-3)releasing the set product in step (b-2).
 24. The method of claim 23,wherein the setting in step (b-2) is performed by applying heat,pressure or UV.
 25. The method of claim 21, wherein the copper- andnickel-plated carbon fiber in step (a) has a chopped shape with a lengthof 3 mm to 500 mm.
 26. The method of claim 21, wherein the product instep (a) further comprises a conductive material selected from the groupconsisting of ferrite, graphite and metal-plated graphite.
 27. Themethod of claim 21, wherein the mixing in step (a) is performed byfurther comprising at least one additive selected from the groupconsisting of a carbon filler, a flame retardant, a plasticizer, acoupling agent, a heat stabilizer, a light stabilizer, an inorganicfiller, a releasing agent, a dispersing agent, an anti-dropping agentand a weathering stabilizer.